As surface mount semiconductor devices having ball electrodes for external connection, packaged semiconductor devices of BGA (Ball Grid Array), CSP (Chip Size Package) and so on are available in which semiconductor elements are electrically connected to circuit boards.
FIGS. 7A and 7B show a conventional BGA semiconductor device. A semiconductor chip (semiconductor element) 2 is die bonded on one of the surfaces of a circuit board 1 that has a circuit pattern and electrode portions on both surfaces. The semiconductor chip 2 is wire bonded with metal thin wires 3 and is molded with resin 4. Solder balls 6 are bonded to electrode portions 5 on the other surface of the circuit board 1. The bonded solder balls 6 act as external terminals (ball electrodes) to be mounted on another circuit board (Japanese Patent Laid-Open No. 2001-144214).
As materials of the solder balls 6, eutectic Sn—Pb solder materials have been conventionally used but lead-free solder materials containing no lead have been increasingly used. Unfortunately, lead-free solder materials reduce a bonding strength between the solder balls 6 and the electrode portions 5.